https://the-federation.info/platform/73 -- try this one instead. Click on the major instances and then check "active users this month" or "posts" or "comments" and you'll see that it's doing quite well in terms of the content snowball.

Estimated active users is about 70k on Lemmy. Not sure about kbin. However, active on Lemmy means posted or commented, so the lurkers should be higher.